The present invention relates to fume cupboards, ventilated cupboards, ventilated cabinets, ventilated hoods and like apparatus (hereinafter collectively referred to as fume cupboards) used for providing aerial containment for gases, vapours, dusts, bacteria and other materials, for example in chemical laboratories.
A fume cupboard is a ventilated enclosure within which operations may be conducted for the purpose of avoiding release of toxic material or the like into a room in which people may be working. The fume cupboard is associated with a fan for drawing air and toxic material from the enclosure for safe discharge, usually to atmosphere, and is also provided with an opening which allows access to the enclosure and through which air is drawn to replace that withdrawn by the fan. A problem with such cupboards however is that the flow of air through the cupboard is not streamlined and eddies are formed, particularly at corners of the cupboard and in the region of the edges of the opening, which results in air and hence toxic material, flowing back through the opening of the cupboard, which is obviously undesirable. It is found that increasing the velocity of air entering the cupboard through the opening helps, to a certain extent, to improve containment and, in this respect, there are recommended air velocities at which cupboards should operate to provide adequate containment. However, simply increasing the air velocities to improve containment is not satisfactory, since above a particular velocity it may be found that containment is actually poorer than at lower velocities. Additionally the use of high air velocities means that more air must be driven from the room in which the cupboard is situated. Obviously, this increases the costs for maintaining the room air at a suitable temperature.